It's on paper that the flow of a map emerges. Flow. Halo 4's designers describe it as an invisible force continually impelling the player onward, and it's a word that recurs again and again in conversation with them. "We tend to describe things based on the idea that the player is a camera, and what the camera sees and what the camera can perceive just running forward without any additional information lets you know where you're able to go," says Pearson.
A map that flows enables players to make intuitive split-second decisions about their preferred route, he explains. "There should be no point where you're forced to do a 180 degree turn to see something to know that you need to go there. Everything needs to be presented to you as you move through the level."
In many ways, flow can be thought of as an absence of frustration on the part of the player, at least so far as geography is concerned. Jumpable gaps are a case in point. "Any time you have a gap, the distances between where you jump from and the other side are either so close that you know you can make it and you recognize that as a route and a place you can flow into, or they're so far apart that you never make the mistake of trying to get somewhere where you can't reach even though it looks like you should be able to."
A million and one factors influence flow, many of them minuscule. As anyone who has spawned at the back of a squad of teammates can attest, even the direction a player faces when she spawns greatly influences where she will go (i.e. almost always forwards, in an almost trance-like state.)
The location of desirable power-weapons and vehicles, which can tip a battle in favor of the player who commands them, inevitably exert a gravitational pull upon gamers. In a thoughtful concession to new players, Halo 4 highlights such items with superimposed markers so that their locations no longer have to be learned through experience.
The flow of play and players on a map will not become evident until testing, which begins as soon as a basic 3D model is roughed or "blocked" out, and continues as the design iterates. To build the 3D maps, Halo developers use proprietary tools developed in-house.
Respawn's Geoff Smith cut teeth designing community maps for Counter-Strike using the Valve Hammer Editor (known as Worldcraft at the time). He made a name for himself with the map De_Karachi01, a map that ultimately launched his map-design career. He would later rebuild it as Karachi for Modern Warfare 2 using Call of Duty mod tool Radiant, a spin-off of id's GNU-licensed GtkRadiant level design tool. "I usually have a pretty clear layout idea before I start using an editor," he says, "even if that layout isn't perfect from the start (they never are)."
"I try to get a level playable as soon as possible. Multiplayer layouts need hours and hours of playtime to make adjustments to make sure the map plays well," he adds. "So there is no time to waste theorizing about how it will play; you just need to get on with it."
Ask designers if there are any metrics they track when developing and testing, it quickly becomes apparent that the initial approach is softer and more intuitive than that. "Early on I am looking for the distances at which people meet: where they stop to shoot at other players and if they can even find each other," says Smith.
Similarly, Halo 4's designers keep a watchful eye on distance. "We definitely have standards for the size than something can be and the time it takes from one corner of a map to the other, or one objective sight to the other," says Pearson. "It's to make sure we're tuning the experience to keep the time-to-death down, or making sure that your time-to-engagement is enough to give you a breather between dying, but not so long that you're hunting through the map and not finding people." Again, game mechanics have a direct bearing. In Halo 3, sprinting was impossible. In Halo: Reach, sprinting was a selectable armor ability. In Halo 4, everyone's at it, and the maps have grown to compensate.
Fundamentally, though, 343 and Certain Affinity simply want to know if maps are fun or not. "Honestly, initially, there aren't a lot of performance metrics we're really looking for," says Clopper. "It's very hard to describe, but when you're in a play-test room and people are moving around a map and having an amazing time there's a sense of fun you can feel in the room. People are yelling, people are having a great time. They're shooting their coworkers. These amazing battles are happening, and that's the great thing about Halo: crazy stuff can happen with the physics."
Further into the development process, Halo 4's developers adopt a more measured approach. "You tend to use the metrics based on playtests to refine the map and define the areas that might have been weaker into more powerful positions," says Pearson. "You never want to have a map that has dead ends or areas of the map that go unutilized, because then it's wasted space and it's not worth the effort of creation. Those tend to get whittled down and worked out so that you start prioritizing areas that get less play to make them just as usable and just as versatile."